If you mean using the socket.io protocol to do JSON-RPC calls, this is supported since both ends can understand and parse json.
You can use e.g. https://github.com//socketio-client-ue4#emit-with-callback and emit and receive calls, the server can use this passed in callback to remotely callback https://github.com//socketio-client-ue4#emit-with-callback-nodejs-server-example. You’d only need to make sure you follow jsonrpc spec (JSON-RPC 2.0 Specification) in your communication.
If you meant doing basic JSON http requests, this is supported albeit not the main focus of the plugin. I’ve added an example for a JSON http post request https://github.com//socketio-client-ue4/blob/master/README.md#http-json-requests.